Wonderful stuff. I remember doing a wave change on a similar HF transmitter at BBC Rampisham. The (very simple) circuit diagram was drawn in pen and ink on a piece of A4 paper outside the transmitter room. The difficult bit was equating inductor symbols with 18" diameter coils of 1/2" copper central heating pipe. The modulation transformer was a bit smaller, though - only about the size of a couple of filing cabinets. The first stage in the modulation amplifier was a Leak TL12+ (10W from PP EL84).

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The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

There are quite a few heritage e-tours around. Some of the most fanatical fans of radio eventually found their way into engineering departments. Here's another one, with a tour of an RCA BTA-50F identical to that at my first station. Sadly it was decommissioned about 10 years ago and likely went to the scrap yard.

Originally posted by rdf Here's another one, with a tour of an RCA BTA-50F identical to that at my first station. Sadly it was decommissioned about 10 years ago and likely went to the scrap yard.

I bought and parted out a complete pair of RCA BTA-10K AM broadcast xmitters about 6 years ago. These were circa 1954. Really nice hardware! There were four attractive heavy cabinets in the lineup. I still have one empty cabinet saved for a project needing a big box, and a whole, untouched RF final cabinet complete with the three output triodesand filament xfmers. It is for sale. An enterprising ham could put a PSU and modulator in the empty cabinet and put this on 160 meters AM. I also have the master oscillators and crystals in the heated ovens. The M.O. used an 807 tube. Heck you could go on the air with good range with just the oscillator!

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"There are more worlds than the one you can hold in your hand." Albert Hosteen, Navajo spiritual elder and code-breaker, X-Files TV Series.